Fiducial markers are useful in various medical applications. In radiation oncology, for example, fiducial markers are placed within or around lesions so that a therapeutic radiation delivery device can track the respiratory motion of the lesion to be destroyed, thereby minimizing damage to healthy surrounding tissue. An example of a radiation delivery device is the Cyberknife® system (manufactured by Accuray Inc., Sunnyvale, Calif.).
Fiducial markers may be placed in a wide variety of anatomies. In certain anatomies such as the lungs, however, placing a fiducial marker is not straightforward even for skilled practitioners. Traditionally, thoracic fiducial placement was performed percutaneously under computed tomography (CT) guidance. However, physicians have reported a 20-40% incidence of pneumothorax during such procedures. See Prevost et al., Endovascular Coils As Lung Tumor Markers In Real-Time Tumor Tracking Stereotactic Radiotherapy: Preliminary Results, European Radiology, 2008. Pneumothorax is a serious adverse, potentially fatal, event.
A minimally invasive procedure to place fiducial markers at locations in the lung is desirable to lower the risk of the above referenced adverse events and to eliminate the need for CT guidance. However, identifying suitable locations for placing fiducial markers bronchoscopically is challenging because of, amongst other things, (1) the limited view provided by an endoscope or bronchoscope, (2) the uncertainty in the marker locations arising from the tidal motion of the lung, (3) the presence of various obstacles such as critical blood vessels in the path to a fiducial marker location, (4) the heterogeneity of the lungs (i.e. the presence of both airways and parenchyma) surrounding the target lesion, and (5) the limitations arising from the particular oncology application to be performed. A system and method that addresses the shortcomings identified above is therefore desired.